在PreferenceActivity中，findPreference()抛出了NullPointerException(Android)。
在PreferenceActivity中，findPreference()抛出了NullPointerException(Android)。
我使用了Kevin Remo在这里给出的答案创建了自己的自定义PreferenceActivity。这段代码没有onPreferenceClickListener，所以我在我的活动的onResume中添加了它。它在API 9上工作得很好，但在API 19上失败了。
以下是我的活动代码。
import android.content.Context;
import android.os.Bundle;
import android.preference.CheckBoxPreference;
import android.preference.Preference;
import android.preference.Preference.OnPreferenceClickListener;
import android.util.AttributeSet;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;
public class SettingsActivity extends CompatiblePreferenceActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
setPrefs(R.xml.user_settings);
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(View parent, String name, Context context,
AttributeSet attrs) {
// TODO Auto-generated method stub
return super.onCreateView(parent, name, context, attrs);
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
Preference logout = (Preference) findPreference("preflogout");
logout.setOnPreferenceClickListener(new OnPreferenceClickListener() {
public boolean onPreferenceClick(Preference preference) {
Toast.makeText(getApplicationContext(), preference.getKey(),
Toast.LENGTH_LONG).show();
return false;
// 在这里打开浏览器或意图
}
});
CheckBoxPreference notification = (CheckBoxPreference) findPreference("prefpushnotification");
notification
.setOnPreferenceClickListener(new OnPreferenceClickListener() {
public boolean onPreferenceClick(Preference preference) {
CheckBoxPreference notification1 = (CheckBoxPreference) preference;
if (notification1.isChecked()) {
notification1.setSummary("通知已开启");
} else {
notification1.setSummary("通知已关闭");
}
return false;
// 在这里打开浏览器或意图
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// 填充菜单；如果存在，则将项目添加到操作栏中。
getMenuInflater().inflate(R.menu.user_setting, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// 在这里处理操作栏项目的单击事件。操作栏将自动处理对主页/上一个按钮的单击，只要您在AndroidManifest.xml中指定了父活动。
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
在onResume中，我使用了findPreference()，在API 19上会出现NPE，但在API 9上工作正常。
这是我使用的支持2x到4x版本的自定义首选项活动类，正如链接中回答中所说。
import android.annotation.TargetApi;
import android.os.Bundle;
import android.preference.Preference;
import android.preference.PreferenceActivity;
import android.preference.PreferenceFragment;
import android.preference.PreferenceScreen;
public class CompatiblePreferenceActivity extends PreferenceActivity {
private int prefs = 0;
// 获取/设置首选项
public void setPrefs(int prefs) {
this.prefs = prefs;
}
// 异常类
protected static class PrefsNotSetException extends RuntimeException {
private static final long serialVersionUID = 1L;
PrefsNotSetException() {
super("\"prefs\"应设置为有效的首选项资源ID。");
}
}
// 创建
@Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (prefs == 0)
throw new PrefsNotSetException();
else
try {
getClass().getMethod("getFragmentManager");
AddResourceApi11AndGreater();
} catch (NoSuchMethodException e) { // Api < 11
AddResourceApiLessThan11();
}
}
@SuppressWarnings("deprecation")
protected void AddResourceApiLessThan11() {
addPreferencesFromResource(prefs);
}
@TargetApi(11)
protected void AddResourceApi11AndGreater() {
PF.prefs = prefs;
getFragmentManager().beginTransaction()
.replace(android.R.id.content, new PF()).commit();
}
@TargetApi(11)
public static class PF extends PreferenceFragment {
private static int prefs;
@Override
public void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(prefs);
}
}
// 修复子屏幕背景故障
@SuppressWarnings("deprecation")
@Override
public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen,
Preference preference) {
super.onPreferenceTreeClick(preferenceScreen, preference);
if (preference != null)
if (preference instanceof PreferenceScreen)
if (((PreferenceScreen) preference).getDialog() != null)
((PreferenceScreen) preference)
.getDialog()
.getWindow()
.getDecorView()
.setBackgroundDrawable(
this.getWindow().getDecorView()
.getBackground().getConstantState()
.newDrawable());
return false;
}
}
堆栈跟踪：
02-13 19:54:08.222: E/AndroidRuntime(4282): java.lang.RuntimeException: Unable to resume activity {com.buzzreel/com.buzzreel.SettingsActivity}: java.lang.NullPointerException
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2774)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2803)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2238)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread.access$800(ActivityThread.java:135)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.os.Handler.dispatchMessage(Handler.java:102)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.os.Looper.loop(Looper.java:136)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.ActivityThread.main(ActivityThread.java:5001)
02-13 19:54:08.222: E/AndroidRuntime(4282): at java.lang.reflect.Method.invokeNative(Native Method)
02-13 19:54:08.222: E/AndroidRuntime(4282): at java.lang.reflect.Method.invoke(Method.java:515)
02-13 19:54:08.222: E/AndroidRuntime(4282): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
02-13 19:54:08.222: E/AndroidRuntime(4282): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
02-13 19:54:08.222: E/AndroidRuntime(4282): at dalvik.system.NativeStart.main(Native Method)
02-13 19:54:08.222: E/AndroidRuntime(4282): Caused by: java.lang.NullPointerException
02-13 19:54:08.222: E/AndroidRuntime(4282): at com.buzzreel.SettingsActivity.onResume(SettingsActivity.java:42)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
02-13 19:54:08.222: E/AndroidRuntime(4282): at android.app.Activity.performResume(Activity.java:5310)